(1) Operation Cord
There is a type of horizontal blind where an endless operation cord is engaged with a pulley which is rotatably supported by an edge of a head box. When operating the operation cord to rotate the pulley, a force is transmitted to a slat drive mechanism in the head box. Thus, it is possible to perform a slat elevation operation and a slat angle adjustment operation. There is also known a technology of operating a vertical blind by rotating an operation cord around a pulley. An operation cord is also used in apparatuses using a windup-type insect screen in place of a sunlight shielding material, elevation apparatuses for up/down window, and elevation apparatuses for laundry pole or the like.
Such an operation cord is an endless cord formed by welding or swaging both ends of a cord which is formed of a synthetic resin in the form of a string (for example, see Patent Documents 1 to 3). As described in Patent Document 4, by engaging such an operation cord with recesses formed on the peripheral surface of a pulley inside a pulley case that houses the pulley, the pulley can be rotationally driven.
(2) Ball Chain
A ball chain may be used as an example of an operation cord.
A ball chain is formed, for example, by molding synthetic-resin balls on a string-shaped, synthetic-resin cord at regular intervals and fixing the balls to the cord. By sequentially engaging the balls with recesses formed on the peripheral surface of a pulley, the pulley can be rotationally driven.
Such a ball chain typically has an endless structure where both ends of a cord having many molded balls attached thereto are coupled together via a connector. For a horizontal blind, where a slat up/down operation is performed by rotating a ball chain about a pulley one or more times, the shape of balls on a ball chain coupling portion and the interval between the balls must be the same as those on other portions.
In such a case, there is proposed a ball chain where a ball on a coupling portion is divided into two portions and the divided portions are fitted with each other to form a ball. (See Patent Document 5)
Where an endless ball chain is suspended from a pulley as described above, the endless edge of the ball chain may be caught on a dweller or another mobile object moving in the room.
For this reason, a coupling portion included in an endless ball chain needs to have a fail-safe function of, when an excessive pull force exceeding a pull force applied in a normal operation is applied to the coupling portion, cutting the coupling portion by means by the pull force to ensure the safety of the dweller and prevent damage to such as the pulley with which the ball chain is engaged. Such a fail-safe function can release the ball chain caught on the dweller or the like to allow the dweller or the like to move, as well as to prevent damage to such as the pulley or the like with which the ball chain is engaged.